Early development of cancer chemoprevention clinical trials: studies of dietary calcium as a chemopreventive agent for human subjects.

Early cancer chemoprevention clinical trials in human subjects had to be carried out with large numbers of subjects studied for long durations, measuring cancer as an end point. However new findings on abnormal epithelial cell growth and development during the multistage evolution of colonic tumors made it possible to carry out chemoprevention clinical trials in several stages, with fewer subjects studied for shorter durations, thus enabling investigators to analyze increasing numbers of chemopreventive agents and nutritional regimens in clinical trials. Supplemental dietary calcium was the first candidate chemopreventive agent studied in this multistage approach in human subjects, as a putative agent for colon cancer prevention. Early- and late-stage intermediate biomarker studies in humans have strongly suggested utility for supplemental dietary calcium to inhibit the development of benign and subsequent malignant colonic neoplasms. Preclinical experimental studies have further demonstrated the ability of increased dietary calcium to inhibit the evolution of colonic tumors when they were induced by targeted mutations, dietary factors, and particularly when given over a long duration of lifespan.